1. Field of the Invention
The present invention relates to an optical scanning device and an image forming apparatus, such as a copier, a facsimile, a printer, or a multifunction peripheral having these functions, including the optical scanning device.
2. Description of the Related Art
In an image forming apparatus, such as copier, a facsimile, a laser printer, or a multifunction peripheral having these functions, using an optical scanning device as a writing unit for forming a latent image on an image carrier such as a photoreceptor, the number of scanning beams used by a scanning optical system of the optical scanning device has increased with increases in speed, resolution, write width, and the like. Furthermore, a color image forming apparatus including a plurality of optical scanning devices using a plurality of beams has prevailed.
As light sources of a plurality of beams mounted on the optical scanning device, a semiconductor laser array in which luminous points are one-dimensionally arranged at a predetermined interval (hereinafter, referred to as a laser diode (LD) array”), a surface-emitting laser array in which luminous points are two-dimensionally arranged at a predetermined interval (hereinafter, referred to as a “VCSEL (vertical cavity surface emitting laser)”), and the like are known. As for the former, there is a method to increase the number of beams by synthesizing beams emitted from a plurality of LD arrays by means of a beam synthesis prism or the like. This can be regarded as light sources in which, similarly to a VCSEL, luminous points are two-dimensionally arranged.
In general, as the number of beams emitted from a light source increases, it becomes difficult to keep an error in the interval between scanning lines formed on a scanned area or a deviation from a mean value of the scanning-line intervals between scanned positions within an acceptable level. If the error or deviation increases, a periodic stripe or non-uniform shading (referred to as ‘banding’) becomes noticeable in a halftone image or a periodic image such as a horizontal line image, resulting in image degradation. Furthermore, in a color image forming apparatus, the increase in the error or deviation causes a color shift (registration error) in each color, resulting in image degradation.
In Japanese Patent Application Laid-open No. H4-101112, Japanese Patent Application Laid-open No. H8-15625, and Japanese Patent Application Laid-open No. 2008-76712, there is described an adjusting means to move a cylindrical lens in a direction of an optical axis of the cylindrical lens or to rotate the cylindrical lens around the optical axis so that an interval between beams on a photoreceptor is adjusted to a target interval, thereby keeping the interval between beams on the photoreceptor and the beam diameter appropriately. However, a means for adjustment of a deviation of the scanning-line interval between scanning positions has not been disclosed.